Electronic organ with tremolo



R. W. CHICK ELECTRONIC ORGAN WITH TREMOLO 4 Sheets-Sheet 1 OriginalFiled Jan. 14, 1947 ll|..||.|lllllllllllllllllllnllll INVENTOR. $1.535;'fl/(k/of,

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' ELECTRONIC ORGAN WITH TREMOLO 4 Sheets-Sheet 2 Original FiQLed Jan.14, 1947 INVENTOR. 5/3552; /1. C'H/CA; BY

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Oct. 30, 1956 R. W. CHICK ELECTRONIC ORGAN WITH TREMOLQ 4 Sheets-Sheet 4Original Filed Jan. 14, 1947 QQN MMERQ United States Patent ELECTRONICORGAN WITH TREMOLO Russell W. Chick, Beverly, Mass., assignor to TheBaldwin Piano Company, a corporation of Ohio Original applicationJanuary 14, 1947, Serial No. 722,049. Divided and this applicationJanuary 23, 1952, Serial No. 267,806

4 Claims. (Cl. 84-115) This application is a division of my copendingapplication Serial No. 722,049, filed January 14, 1947, and entitledElectronic Organ, now abandoned.

My invention relates to electronic musical instruments and in particularto oscillator systems adapted to produce musical tones, together withcooperating structure and auxiliary circuits.

The so-called electric organs heretofore produced have relied in generalon gear-driven tone wheels or similar electro-mechanical tone generatingdevices. The most important object of my invention is to produce musicalnotes entirely by electronic means with the ultimate purpose ofproducing more satisfactory tones at less cost.

Another object of my invention is to provide means for locking aplurality of oscillators in fixed frequency relationship in which theseveral oscillators produce different frequencies but in a definite andstable relationship.

A further object of the invention is to prevent factors such astemperature changes and changes in the values of circuit components fromcausing frequency drifts in the oscillators of an electronic organ.

Another object of the invention is to provide an electronic organ inwhich a large number of notes may be placed in proper tuned relationshipby means of a very small number of adjustments. For example, in aneightyeight note instrument it is one objective to tune the entireinstrument by properly tuning twelve inductances.

One important feature of the invention resides in a master oscillatorprovided with automatic frequency stabilizing means.

Another feature of the invention resides in the combination of a stablemaster oscillator and a plurality of slave oscillators loosely coupledand arranged to oscillate at harmonics of the frequency of the masteroscillator.

Another important feature of my invention relates to a novel transformerused for coupling the slave oscillators to each other and to the masteroscillator.

Still another feature of the invention resides in a novel circuit withan associated automatic control system for producing a tremolo orvibrato effect by modulating the output of the final amplifier at arelatively low frequency.

These and other objects and features of the invention will be morereadily understood and appreciated from the following detaileddescription of a preferred embodiment thereof selected for purposes ofillustration and shown in the accompanying drawings in which:

Fig. 1 is a circuit diagram for the master and slave oscillators,

Fig. 2 is a view in perspective of the coupling transformer,

Fig. 3 is a view in side elevation of the transformer,

' Fig. 4 is a plan view of the transformer,

Fig. 5 is a view in end elevation of the transformer,

Fig. 6 is a circuit diagram of a second form of stable masteroscillator, and

Fig. 7 is a circuit diagram of a tremolo circuit.

General organization The electronic organ of my invention comprises anumber of master oscillators arranged to produce audiofrequencyoscillation of great stability, each master oscil-- lator being coupledto a plurality of audio oscillators tuned to subharmonics of the masteroscillator frequency and triggered or synchronized by the master so thatall the oscillators are locked at predetermined frequencies. Theoscillators are designed to produce notes very rich in harmonics. Anamplifier and speaker are provided and connected to be driven from theoscillators through a special filter which can be adjusted to removevarious percentages of the harmonics or add further harmonics in orderto produce final notes of varying timbre in simulation of theinstruments of the orchestra. A keyboard having a key for eachoscillator is, in effect, a switchboard determining which oscillator, orcombination of oscillators, is connected to the amplifier. A specialcircuit is coupled between two of the oscillators and the amplifier andarranged to modulate the amplifier by the difference of the frequencyproduced by beating together the output of the two oscillators. Theresult is a pleasing tremolo or vibrato effect.

With this general explanation in mind the following detailed descriptionof some of the elements of the organ will be better understood.

7 he master oscillator The master oscillator is organized about thetriodes V1 and V2 as shown in Fig. l and comprises essentially a Wienbridge oscillator, generally recognized as a special form of an RCoscillator. Inasmuch as the master oscillator is to fix the frequency ofas many as eight toneproducing oscillators, as will later be described,it is imperative that the frequency of the master oscillator be stable.if the frequency drifts, it is not a question of detuning one note; itwill affect an entire group. If one note of an instrument is out oftune, the effect is not too serious, but if several notes are out oftune, the result is apparent even to the most unmusical listener.

Those skilled in the art will readily appreciate that the resistorgenerally connected in series between the grid of V1 and the couplingcondenser C3 leading to the plate V2 has been replaced by an inductanceL1, in Fig. 1, preferably a high Q, low resistance coil. It will befurthermore appreciated that the frequency of the oscillator may bevaried by changing one or more of the circuit elements R2, C1, or C3.The frequency of oscillation, assuming that the amplifier tube V2 haszero phase shift, is given by the equation:

resistor R1). if all the resistors and all the capacitors are equal, theequation becomes:

1 fines Any one of the circuit elements referred to in the equations maychange in value as a result of change in the ambient temperature.Furthermore some of the elements may change in value with age. It can beshown by experiment as well as mathematically that a decrease in thevalue of R2, C1 or C3 will produce a corresponding increase in thefrequency of oscillation. Conversely an increase in the value of R2, C1or C3 will reduce the frequency of oscillation. Furthermore if animpedance be connected in the position of L2 in Fig. l, the frequency ofoscillation will increase as the impedance of L2 is lowered. It has beenestablished that the impedance of a coil increases with increases infrequency. Hence by inserting the inductance L1 between the grid of V1and the coupling condenser leading to the plate of' V2, I insert in thecircuit an element tending automatically to compensate for frequencydrift likely to be encountered" in the operation of the oscillator.If'the frequency tends to increase as the result of a lowered value ofR2, C1. or C3,.the immediate result will be an increase in the impedanceof Llwhich in turn lowers the frequency of'oscill'ation.

For; additional frequency stabilization I have connected L2 in shuntwith L1 and R2, the grid bias resistor for V1. One function of'L2 is tovary the shunt impedance across .R2' and L1 in the following manner. Ifthe frequency of the circuit shouldtend to rise, the impedance of L2also rises, and consequently reduces the frequency of'the oscillator. Byproper selection of the value of L2, the correct amount of compensationmay be introduced. Another function, of the coil L2 is to control theamount of regenerative feed-back reaching the control grid of the tube,V1, As the impedance of the inductance L2 increases with an increase infrequency, the amount of feed-back voltage increases; the increase infeed-back voltage in turn reduces the frequency of oscillation.

Furthermore, should the frequency of oscillation decrease, the impedanceof L2 likewise decreases, thus decreasing the shunt impedance across R2.and L1 and resulting in an increase of frequency of the oscillator.Accordingly it will be seen that I have provided means for stabilizingthe frequency of the oscillator against factors which would otherwiseresult in varying the frequency either up or down over a narrow range.

Inasmuch as the frequency is afiected by changes in thevalue of thecondenser C1, I prefer to employ a silvermica. condenser or any suitablecondenser exhibiting practically zero temperature coefificient.Beneficial results will be obtainedif all the circuit components areselected for minimum temperature coefficients.

It is to be understood that while I have invented a stable oscillatorfor supplying the triggering or synchronizing. impulses to the slaveoscillators, my invention also relates to the combination of a source oftriggering impulses of stable frequency and the slave oscillatorscoupled by anovel form of transformer for operation at the fundamentalfrequency of the master and harmonics or-sub-harmonics thereof.Consequently the master oscillator. may take many forms, includingmechanical or electro-mechanical sources of oscillations. The masteroscillator shown in Fig. l is satisfactory. In Fig. 6 I have-shownanother form of master oscillator which I have found preferable forreasons of economy and becauseit-is inherently more stable. Furthermorethe frequency isnot affected by line voltage variations of as much as150%.

In general organization the master oscillator shown in Fig. 6 is what isgenerally referred tons a two-terminal oscillator. That is to say, asecond triode is used as a phase inverter in place of the moreconventional tickler coil. As shown, the oscillator is formed about adual triode 80, for example a 6SN7. The plates are supplied from B+through a pair of plate load resistors 82, a filter condenser 84 beingconnected across the line to smooth out ripples. The grid of the secondtriode is connected through a coupling condenser 86 to the plate of.the'first triode, and the plate of the second triode is connectedthrough a coupling condenser 83 and a resistor 90 to the grid of thefirst triode. The condenser 88 and resistor 90 supply the necessary feedback voltage to the. grid of the first triode to maintain oscillation.In the. grid-cathode circuit of. the first triode there is connected atank circuit including a variable inductance coil 92 and a. condenser94. For temperature stabilization the. condenser 94 is preferably of thesilver-mica type or. other construction displaying a negligibletemperature coefiicient- The cathodes are biased conventionallyby.means. of, a pair ofresistors 96. A condenser 100.-is.placedphysically,adjacent the condenser 88 and issubject to the same temperature effects.It is connected. to;g rotlnd;andto,thejunctionof.v the condenser 88 andthe;

I sistance 4, resistor 90. The ratio between charges on the condensers8S and will remain very nearly constant in spite of temperature changesand their joint function is to maintain the feed-back voltage constant,thus tending to prevent frequency drift.

The capacity of the condenser 94 is purposely made high, i. e. 20,50,000mmfd, in order to minimize input tube capacity effects which may beabout 3.0 mmfd. Changes in tube capacities are thus minute in comparisonwith the tank circuit capacity and have no effect on the frequency ofthe output. Q coil with minimum'D. C. resistance.

The resistor 90 not only provides the feed-back path but also tends toisolate the tuned circuit from variations in tube characteristics andvoltage variations, the effects of long use of the tubes, etc. Indetermining. the value of the resistor 90 a number of factors must berecognized, including the rnu of the tubes, the plate resistance, andthe resistance offered by the tank circuit. The critical value is givenby in which, Re. is the critical value of the resistor 90.; RL is theimpedance of the tuned. circuit at resonance in shunt with thegrid-cathode impedance of V1; 1: is the amplification factor of thetube, and Rp is the plate re.-

It follows therefore. that by employing high resistance of. Re, the.feed-back voltage will change very little if at all-in response. to.changes in RL, u, or Rp. Consequently I. use a resistor 96 of 500,000 to1,000,000 ohms.

To recapitulate somewhat, the two-terminal oscillator shown in Fig. 6'isrendered satisfactorily stable by the combination of the condenser 190connected as shown and disposed adjacent the condenser 38; the highresistance it and the silver-mica condenser 94.

The oscillator shown in Fig. 6 is provided with a line 1&2 leadingfromB+ to the first winding on the transformer shown in Fig. 1, cathode ofthe second half of. the triode 8% to the grid of the tube V3 of Fig. l.and including an, isolating. resistor 1635 and a coupling condenser 06.The. line 108 is a ground connection. A filter condenser 11%? isconnected from the 8 supply line 102 to ground as line 108.

The slave system The output of the stabilized oscillator is taken fromthe cathode of the amplifier tube V2 and fed to the grid of a triode V3connected as a buffer and amplifier and including in its plate circuit acoil. 10 wound about one end of a long'core 12; The output is taken fromthe coil 1% through a blocking condenser l l and a series resistor 1610a binding post 18 mounted in a strip 20.

As shown in Fig. 1 the. core 12, in addition to the coilltl-has sixotherwindings 22 each of which is included in the grid-plate circuit of. aconventional blocking oscillater. The blocking oscillators are organizedabout triodes'Vt, V5,.V6, V7, V8. and V9 and are all alike except thatvthe circuit constants are varied. For example. the. frequency. of themaster oscillator may be fixed at 3520C. P. S. and the blocking.oscillators set at. sub-multiples i. e. V4l760; V58 80; V6440; V7220;Vii-110 and V955. The assembly shown in, Fig. 1. will therefore produceseven notes each an octave apart and provide the As for an organ. Icontemplate providing. other assemblies to produce the other notes ofthe chromatic. scales. The number of notesv is not critical .and. isentirely amatter of choice; eighty-eight notes. isythe, conventionalnumber.

The master oscillator and all the slaves, produce notes rich inharmonics; by means of. ancillary circuits (not shown) I may removevarious percentages of certain harmonics and thus provide means forsimulating accuratelyv the timbre. of .many instruments ofthe orchestra.

Itis. not necessary that eachslave per. se. be precisely The coil 92'should. be a high" a line 1 34 leading from the,

tuned to oscillate at the required frequency. By choosing the circuitcomponents to make each slave oscillator oscillate near the requiredfrequency, I achieve the desired result. The impulses from the masteroscillator act as trigger impulses and lock the slave oscillatorssuccessively at the required frequencies. This is an important featureof the invention because it permits the slave oscillators to beassembled with relatively inexpensive components and with sidetolerances. If the master oscillator is set to produce impulses rich inharmonics about a fundamental of 3520 C. P. 5., and the first slaveoscillator V4 will naturally oscillate at about 1700 C, P. S., theeffect of the master oscillations inductively coupled into thegrid-plate circuit of the oscillator V4 will be to change the frequencyof the latter at once to 1760 C. P. S., and the master oscillator thusoperates to synchronize or look the slave oscillator at the requiredfrequency.

The coupling between adjacent coils of the transformer is such that theamplitude, say, of the fundamental frequency in L3 is much greater thanit is in L4. In L4 the amplitude of the sub-harmonic of the fundamentalis much greater. So, in L5 the sub-harmonic of the frequency'of theoscillator V5 is much greater in amplitude than that of the firstsub-harmonic in V4. In other words the locking is a cascade effectwitheach oscillator supply triggering impulses to the next one in line.

It is preferable to set the master oscillator at the highest frequencyof the series of notes to be produced in the assembly. A change of onecycle per second in the trigger frequency of the master oscillator willbe reflected in a change of only at the lower end, in the oscillator V9.On the other hand if the master oscillator was set at 55 C. P. S., achange of one cycle per second in the master oscillator would produce achange of 64 cycles in the high note of the assembly. A frequency shiftof one cycle out of 3520 C. P. S. is not detectable by the human ear,but a change of 64 cycles is immediately evident, even at 5,000 C. P. S.

The transformer The success of the system depends in part upon thedesign of the transformer used to couple the master oscillator to theslaves and the slaves to each other. For one thing the amount ofcoupling is fairly critical. If the coupling is too close, all of theoscillators will operate at the same frequency. If the coupling is tooloose, the desired locking effect is not obtained. I have found that atransformer constructed as shown in Figs. 2-5 may be used to greatadvantage. The transformer is organized about a special core formed offiat rectangular plates made of silicon steel about .014 thick. I havefound that a silicon steel well suited for the purpose is sold under thetrademark Trancor. I provide a number of long plates 50 formed as twospaced stacks in which the plates are separated by short transverseinterleaved stacks of silicon steel plates 52. Consequently the plates50 are separated from each other by air gaps except at the areas shownwhere the alternate longer transverse stack plates 52 are interleaved. v

In order to avoid too close coupling between successive blockingoscillators, I prefer to leave a wide gap in the centers of the longstacks on each side of the transformer. To obtain this effect I leaveout three long plates in the center of the long stacks. The effect isthat the three inner plates are discontinuous, thus providing a largerair gap and consequent looseness in the coupling. Various combinationsmay be employed, and the specific arrangement shown in the drawings isto be considered as exemplary only. The assembly of the plates 50 and 52is secured by any suitable fastening. About each one of the stacks ofthe plates '52 there is wound a coil contained between a pair of endplates 60 and provided with soldering lugs 62 attached to the ends ofthe coil and a soldering lug 64 attached to the center of the coil for acenter tap connection. Each coil is covered by a protective layer 66 oftreated fabric or paper. The winding of one of the coils is suggested inFig. 4 at the left end thereof where the covering 66 has been brokenaway to expose the windings 68. The several coils are spaced apart equaldistances by air gaps between successive covering layers 66. Thisconstruction provides just the right amount of coupling. :In a typicalassembly, referring again to Fig. '1, the coils D3 and L4 may comprise8,000 turns of No. 40E wire; the coils L5, L6, L7 and D8 may comprise10,000 turns of No. 40E; and the coil L9 may comprise 13,000 turns ofNo. 40E. Condensers C5 and C6 may be .01 mfd.; 07 may be .02 mfd.; 08may be .03 mfd; and C9 and C10 may be .1 mfd. The grid bias resistors 15may then be given the values appropriate to set the slave oscillators ator near the required frequencies, in accordance with establishedpractice.

One of the novel features of my invention resides in a circuit arrangedto produce a tremolo or vibrato effect by varying the output volumerapidly. The preferred form of the tremolo circuit is shown in Fig. 7. Apair of triodes V8 and V4 are connected with parallel cathodes andplates and arranged otherwise as conventional amplifiers having somedegree of non-linearity so that intermodulation products may be producedfor purposes to be explained hereinafter. The control grids are fed fromthe cathodes of two of the slave oscillators of the type shown in Fig.1, the slave oscillators being so chosen that a beat'frequency ofroughly seven cycles per second is obtained on the plates of V3 and V4.For example, the slave oscillator producing All at 116.5 C. P. S. may beused in conjunction with the slave producing B at 123.5. The output fromthe triodes V3 and V4 will therefore contain a beat frequency of 7 C. P.S. as well as 116.5 C. P. 8., 123.5 C. P. S., and 240 C. P. S. as aresult of the non-linearity of the amplifier tubes the V3 and V4.Conventional grid bias and cathode bias resistors are shown as well as acathode bypass condenser.

The primary winding of a transformer T9 is connected in the platecircuit of the parallel triodes V3 and V4 with a condenser C44 shuntedacross the primary. The secondary of the transformer T9 is shuntedacross a condenser C47 and connected to the cathode, control, screen, orsuppressor grid (not shown) of one of the tubes in an amplifier 200 andto ground. The values of the condensers C44 and 047 are chosen to offervery high impedance to frequencies of the order of 760 C. P. S. and verylow impedance to higher frequencies. Consequently it is only the beatfrequency of 7 C. P. S. which passes through the transformer T9 and isapplied to the amplifier 200.

A manually controlled switch 202 is provided to shortcircuit the outputof the transformer T9 when no tremolo effect is desired. In parallelwith the switch 202 is a relay-controlled switch 204, the circuit forwhich will now be discussed.

If the tremolo circuit were continuous in its operation upon the openingof the switch 202, there would be an objectionable pulsing effectaudible to the listener when no keys were depressed and the instrumentsupposedly silent. Therefore I provide means for short cirouiting thetremolo circuit output when no key is depressed; however, it is notdesirable to have the tremolo effect shut off for the momentary pausesduring the playing of a composition, as for example, during quarter orhalf rests. Accordingly, I provide time delay means for retaining thetremolo effect for a short time after a note has been played and allkeys released.

The time delay relay circuit is organized about a double triode V5 andV6 and a relay 206 controlling the switch 204. One side of the relay 206is connected to the primary winding of the transformer T9 which in turnis connected to B+. One half V5 of the double t-riode is connected as adiode rectifier, the grid and plate being tied together and connected toone side of the output transformer T6 associated with the amplifier 200.and connected across a speaker 20.8. The cathode ofithe-triode V isconnected to the grid of. the triode V6. ode of the triode V6 is biasedfrom avoltage divider R 90 and R91 connected from 3+ to. ground, thebias being such that the triode V6 is cut off except when the triod'e V5is conducting. The grid circuit of the triode V6 includes .a resistorR92 shunted across acondenser' C46,. and the plate is connected to therelay206. A cathode bypass condenser C49 is also provided.

sNorma-lly'the switch 204 is closed to short circuit the output of thetremolo circuit and the relay is deenergized. When a key is depressed,the amplifier 200 is driven and the transformer T6 carries current. Thediode V5 then delivers positive bias for the grid of the trio'de V6which consequently becomes conducting and. energizes the relay 206 toopen the switch 204 and permit the sevenrcycle amplitude modulation ofthe amplifier 200 from the transformer T9.

When all keys are released, the transformer T6 delivers no -A. C.voltage to the tube V5 and the tube V6.

is then cut off by cathode bias supply. However, the swing to beyondcut-oft is delayed by the charge on the condenser C46 which graduallyleaks off acrossthe' re:- sistor R92 at a rate determined by the RCconstant of C46 and R92. The time is therefore proportional to thevalues of C46 and R92. When the condenser C46 has been discharged, thetube V6 is cutoff and the relay 206 is 'de-energized; the switch 204 isclosed, and the tremolo circuit is out 01f.

It should be understood that any convenient beat frequency may beobtained by choosing different slave oscillators to drive the tubes V3and V4. Also I may pro vide a switch to select two out of three slaveoscillators so that the player may select a fast or slow tremolo. Forexample, the circuit maybe organized to provide a. choice between aseven-cycle tremolo or a fourteen-cycle tremolo.

As with nearly all electronic devices it is possible to substituteequivalent circuits or portions of circuits in a device employing. acombination of electronically performed functions. I believe thefunctions performed by the apparatus shown and described form. a novelcombi nation; I believe also that the particular master oscillator andtremolo circuits shown are novel per se aswell' as the physicalstructure of the transformer shown in the drawings. Some of the appendedclaims are expressions of my novel combinations of functions; other arespecific to the details of the circuits or elements they describe. Icould not, Without a fantastic multiplication of claims, drawings, andwords, describe all the modifications and equivalents known to me. Acompetent electronic engineer will understand them and be able toproduce an instrument embodying my invention.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

1. In an electronic musical instrument including an amplifier, a pair ofsources of different electric audio frequency oscillations, electronicmeans connected to said- Sources for beating said oscillations together,a tuned cir- The bath cuit connected to said electronic means forpassing only the difierence frequency, connections between saidamplifier and said tuned circuit, a switch controlling said connections,a relay controlling said switch, a rectifier connected to the outputofsaid amplifier, an amplifier tube having a control grid connected tosaid rectifier and normally biased beyond cut-01f, the plate of theamplifier tube being connected to said relay, the circuit being soarranged-that when said amplifier is producing, said rect-ifier deliverspositive bias to said amplifier tube to render it conducting, and aresistor-condenser combination included in the grid-cathode circuit ofsaid amplifier tube to delay the cutting off of said tube and theconsequent de-energization of the relay when the rectifier stopssupplying positive bias to the control grid of said amplifier tube.

2. An electronic musical instrument comprising a plurality of sources ofaudio-frequency oscillations, two of said sources differing in frequencyby a desired low modulating frequency, a non-linear impedance networkhaving two input circuits and an output circuit, said two input circuitsbeing connected to said two sources, an output system for convertingaudio-frequency oscillations to sound, a keyboard system connectedbetween said plurality of sources and said output system for selectingand linearly combining oscillations from said sources, modulation meansconnected between said output circuit of said. non-linear network andsaid output system for modulating at said low modulating frequency theoscillations selected and combined by said keyboard system.

3. The combination claimed in claim 2, including a switching circuitconnected to said non-linear impedance network for deactivating itseffect on said output system.

4. The combination claimed in claim 3, including a time delay relaycircuit in parallel with said switching circuit and connected to saidoutput system, operative upon a cessation of said oscillations to delaythe deactivation effect on said output system.

References Cited in the file of this patent UNITED STATES PATENTS1,854,986 Fitch Apr. 19, 1932 2,110,082 Granger Mar. 1, 1938 2,247,544Daily July 1, 1941 2,274,992 Nelson Mar. 3, 1942 2,328,282 Kock Aug. 31,1943 2,406,932 Tunick Sept. 3, 1946 2,470,705 Larsen May 17, 1949'2,485,538 Rowe Oct. 18, 1949 2,490,448 Lott Dec. 6, 1949 2,500,820Hanert Mar. 14, 1950 2,534,342 Daniel Dec. 19, 1950 2,539,826 GeorgeJan. 30, 1951 2,569,426 OBn'en Sept. 25, 1951 FOREIGN PATENTS 237,280Switzerland Aug. 1, 1945 OTHER REFERENCES Radio Engineers Handbook, byTerm-an, 1st edition, 1943, pages 567-569.

